Inkjet printers are known as liquid ejecting apparatuses of one type. Known inkjet printers include a serial type which applies ink droplets ejected from a head onto printing paper while moving the head in the width direction of the printing paper and which feeds the printing paper perpendicularly to the width direction of the printing paper, and a line type which has a line head extending along the entire width of printing paper, which feeds only the printing paper perpendicularly to the width direction thereof, and which applies ink droplets ejected from the line head onto the printing paper.
The head includes a plurality of nozzles for ejecting ink droplets. In the line type, the nozzles are typically not arrayed in line in the width direction of the printing paper. For example, nozzles are arranged along a line inclined with respect to the feeding direction of printing paper, as is disclosed in Japanese Unexamined Patent Application Publication No. 2002-36522.
More specifically, as shown in FIG. 6 of Japanese Unexamined Patent Application Publication No. 2002-36522, nozzles 31 are not arranged straight perpendicularly to the feeding direction of a sheet 14 (in a direction shown by a one-dot chain line in FIG. 6 of Japanese Unexamined Patent Application Publication No. 2002-36522). The first to seventh nozzles 31 are arranged in a direction declining to the right with respect to the direction shown by the one-dot chain line.
The nozzles are arranged in the above manner for the following reason:
FIG. 11 is a view showing the positional relationship between the arrangement of nozzles 1 to 4 of liquid ejecting parts, and dots formed on printing paper. In FIG. 11, the nozzles 1 to 4 are arranged in line (in a straight line) in a head. This direction is defined as an X-direction, and a direction perpendicular to the X-direction is defined as a Y-direction. Therefore, the printing paper is fed in the Y-direction. In FIG. 11, the head is fixed, and only the printing paper is fed in the Y-direction (downward).
During printing, the printing paper is continuously fed in the Y-direction (downward) in the figure. Simultaneously, ink droplets are ejected from the nozzles 1 to 4 of the liquid ejecting parts, and land on the printing paper.
Ink droplets are ejected from the nozzles 1 to 4 of the liquid ejecting parts at a plurality of different times, and all the liquid ejecting parts are not simultaneously driven to eject ink droplets. Although a plurality of liquid ejecting parts are simultaneously driven, adjoining liquid ejecting parts are not selected as liquid ejecting parts that are simultaneously driven.
Normally, ink droplets are simultaneously ejected from a plurality of liquid ejecting parts. Liquid ejecting parts to be selected in this case are apart from one another to some extent. When an ink droplet is ejected from one liquid ejecting part, vibration caused by the ejection is transmitted to an ink chamber and an ink channel, and has an influence on the adjoining liquid ejecting part.
This influence appears as a change of a meniscus (position of an ink surface in the nozzle). If an ink droplet is ejected in a state in which the meniscus is changed, the size of a landing dot changes. In order to avoid this situation, control is executed so that, when an ink droplet is ejected from one liquid ejecting part, an ink droplet is not ejected from an adjoining liquid ejecting part until the change of the meniscus is removed. As liquid ejecting parts that simultaneously eject ink droplets, liquid ejecting parts disposed at separate positions are selected.
When ink droplets are ejected by simultaneously driving all the liquid ejecting parts, the instantaneous power consumption is extremely high. Therefore, such driving is not performed.
FIG. 11 shows that ink droplets are simultaneously ejected from the same-numbered nozzles 1 to 4. Moreover, control is executed so that ink droplets are sequentially ejected from the nozzles 1 to 4 in increasing numerical order.
Accordingly, ink droplets are first ejected from two nozzles 1 (the first and fifth from the left) to form dots D1 on printing paper. When a predetermined time elapses after that time, ink droplets are ejected from two nozzles 2 to form dots D2 on the printing paper. Further, when the predetermined time elapses after that time, ink droplets are ejected from two nozzles 3 to form dots D3 on the printing paper. Furthermore, when the predetermined time elapses after that time, ink droplets are ejected from two nozzles 4 to form dots D4. In this way, eight dots D1 to D4 are arranged on one line.
In this case, when it is assumed that the time from when ink droplets are ejected from the nozzles 1 to form dots D1 on the printing paper to when ink droplets are ejected from the nozzles 2 to form dots D2 on the printing paper is represented by t (that is, the predetermined time is t) and the feeding speed of the printing paper is represented by v, the moving distance x of the printing paper during the time t is given as follows:X=v×t 
That is, as shown in FIG. 11, the distance (displacement) between the dots D1 and D2 in the Y-direction (feeding direction of printing paper) is equal to the above distance x. This also applies to the distance between the dots D2 and D3, and the distance between the dots D3 and D4.
Although forming positions of dots (landing positions of ink droplets) shown by dotted circles in FIG. 11 are ideal, actual dots are formed at the positions shown by diagonally shaded circles, and the dots D1 to D4 are not arrayed on a line parallel to the X-direction.
As a result, an actually formed image is not an exact straight line, but is a serrated pattern. This phenomenon similarly occurs not only when a straight line is formed, but also when other patterns are formed, and lowers print quality.
Accordingly, the nozzles 1 to 4 of the liquid ejecting parts that perform ejection at different times are conventionally not aligned in the Y-direction, as shown in FIG. 12. The distance between the nozzles 1 and 2 in the Y-direction is equal to the above-described distance x. This also applies to the distance between the nozzles 2 and 23, and the distance between the nozzles 3 and 4. Each two nozzles 1, 2, 3, or 4 are disposed on a line parallel to the X-direction.
With this arrangement of the nozzles 1 to 4, even when ink droplets are sequentially ejected from the nozzles 1, the nozzles 2, the nozzles 3, and the nozzles 4 at different times, all dots D1 to D4 can be placed on a line parallel to the X-direction on the printing paper.
In the above related art, however, when a plurality of nozzles 1 to 4 of the head are arranged in a form other than the linear form, as shown in FIG. 12, first, production cost increases.
Secondly, a process of inspecting the positions of the nozzles is performed after the production of the head, the inspection is performed by image recognition, and therefore, when the nozzles are arranged in a form other than the linear form, the inspection time is longer than that for nozzles arranged in a linear form. The production cost is thereby increased.
Thirdly, when the nozzles are arranged in a form other than the linear form, as shown in FIG. 12, sharing of the head is impossible. For example, the distance between the nozzles 1 and 2 in the Y-direction in FIG. 12 is determined to be equal to the above-described distance x. However, since the distance x is a function determined by the feeding speed of the printing paper in the Y-direction in the printer and the time t, the use of the head in which the distance between the nozzles 1 and 2 in the Y-direction is determined beforehand limits the feeding speed of the printing paper and the time t.
Fourthly, although the four types of nozzles 1 to 4 are arranged so that the nozzles of each type are aligned on the same line in the X-direction in the example shown in FIG. 12, in a case in which the positions of the nozzles are determined beforehand, when ink droplets are ejected at different times, they can always be ejected only in the order based on the nozzle arrangement.